1. Field of the Invention
The present invention relates to an ink jet printer, and, more particularly, to a method of printing with high resolution using an ink jet printer.
2. Description of the Related Art
An ink jet printhead includes a plurality of nozzles arranged vertically, i.e., in the paper feed direction, with respect to a printed page. The nozzles have a fixed vertical spacing between them, such as 1/600 inch for a 600 dots per inch (dpi) printhead. Additionally, the array of nozzles travels horizontally repeatedly across the page, with some amount of advance of the paper in the vertical direction between such scans, dropping dots at a fixed horizontal distance, which can also be 1/600 inch. The term “horizontal”, as used herein, indicates the direction of printhead scan, perpendicular to the vertical, paper feed direction. According to the present example, the vertical pitch of the nozzles, in combination with the horizontal distance between dots as they are placed on the page, define a printing grid, or matrix, of a given vertical and horizontal resolution.
Typically, the combined behavior of the horizontal scanning of the nozzle array and the amount of vertical paper feed between consecutive scans allows exactly one drop of ink to be placed at every pixel position of the printing grid. In this condition, the grid is said to be “perfectly covered.” Each pixel position has one opportunity to be printed on exactly one scan of the printhead and by exactly one nozzle of the printhead.
The well known technique of “shingling” employs a method whereby the printing grid is “super covered”, meaning that the horizontal scanning behavior and the vertical paper feed allow that each pixel position has multiple opportunities in which a drop of ink can be placed at that position. Typically, these multiple opportunities are available in different scans of the head, which implies that the multiple opportunities are realized by different nozzles of the printhead.
A problem is that multiple passes of the printhead over the same raster line decreases the print speed of the printer. Another problem is that the amount of information that can be transferred to the print medium is limited by the fact that only one size of ink drop can be deposited on the print medium. Thus, only through the selection of locations at which the single-sized ink drops are deposited can the information be conveyed to the print medium.
What is needed in the art is a method of transferring more information to the print medium without requiring more passes of the printhead.